Radio direction finder



Filed April 30, 1946 VIDEO AMPLIFIER RECEIVER BLOCKING OSCILLATOR G W R.T ,7 E ll DW m m m m t] Gul g MW 2 LPN 1 O MO 5 7 v0 3 2 E W DGU wNC mm EC M m R My mm Huewm a no m Mm HG .nvR mm D nvvzlvrom PAUL A. PEARSON 3y ATTOR Y Patented Nov. 10, 1953 UNITED RADIO 'DIKE QN FINDEIP Paul A. Pearson, Seattle, Wash, assignor to Unit at of Am as epresented by he Secretary of War Application April 30, 1946, Serial No. 665,989

This invention relates enerally to electrical apparatus and more particularly to a direction indicating system.

Some previous direction indicators actuated by the reception of radio frequency pulsed signals employed a cathode ray tube or rotating antennas, or a combination of both. The use of either is undesirable especially when these devices are used in aircraft. Regardless of where used, a cathode ray tube has such disadvantages as fragility and the requirement of high voltages. In any type of installation a fixed antenna is less subject to mechanical and electrical difliculties than a rotating antenna. Selsyns, synchronous motors or other similar devices With their attendant angular lag, hunting for synchronism and mechanical load rescnances are usually required as auxiliary equipment for rotatable antennas.

Previous direction indicating systems have also utilized rotatable loop antennas in conjunction with an indicating meter for determining the antenna pattern null positions; such systems also have some of the disadvantages already mentioned.

It is an object of the present invention to pro.- vide a direction indicatin system without the use of cathode r y tubes or rota i an n s.-

It is also. an object o provid a direc ion india in syst m which. w ll operate on either con.- tinuous wave signal r pulsed s n ls.

It is anot r ob ect to prov d a impl l t weight direction indicating system utilizing an indicat n m r icu a y adapted for us in a c aft, f r co t uo s nd catin th direction of a received signal relative to. the heading f the aircra t- In general a direction indicating system which will accomplish the above mentioned objects comprises a lobe switching antenna, a receiver, charging circuits, discharge circuits, and an indica in me More specifically, a lobe switching antenna having its main axis in line with the airplane a ds, receives a signal which is amplified by a radio frequency amplifier and a video amplifier. Video signals are then alternately fed to two identicaldiode remembering circuits whose output voltages are received by a voltage comparison circuit. The voltage difference of these two signals feel to the voltage co'rnparisgn circuit operates an indicating meter tosho-w the airplane heading with respect to the bearing of a received signal.

A control circuit comprising a blocking oscil- 2 later and two identical discharge circuits is provided for discharging the two previously mentioned diode remembering circuits.

Other objects, features and advantages of this invention will suggest themselves to those skilled in the art and will become apparent from the following description of the invention taken in connection with the accompanying drawing which is a block diagram of an apparatus embodying the principles of this invention.

Referring now to the single figure of the drawing, a lobe switching antenna i9, aligned along the axis of the aircraft, alternately passes signals from its two lobe elements to receiver ll. Lobe switch l2 alternately connects the two lobe elements of antenna Hi to receiver II at a rate of a few hundred cycles per second. Received signals are further amplified in a video amplifier i3 and are then fed through a second lobe switch Hi to two identical circuits l5 and I6. Lobe switches l2 and'l4 operate in synchronism such that diode remembering circuit i5 operates on signals received by one section of lobe antenna i0, and diode remembering circuit I B operates on signals received by the other section of lobe antenna iii. A voltage comparison circuit receives the two output voltages of circuits l5 and I6 and the voltage difference, if any, of these two outputs is applied to an indicating meter i8.

A control circuit consisting of a blocking oscillator l9 and'two identical discharge circuits 20 and 2| is'also actuated by video signals from video. amplifier I3, Circuits 28 and 2! provide voltages for discharging circuit elements of diode remembering circuits [5 and I6, respectively.

The principle of operation of this system depends upon the relative magnitude of signals received by the two lobes of antenna l0. When a signal is received from a transmitter straight ahead of the airplane, signals of equal amplitude are received by the two lobes of antenna Ill; a mp is n o the ener co en o t wo Sianals results in a difference energy of zero, and the pointe 9i indicat n meter l8 m s ntered, However, if a signal is received from a tra smitte whi h is o in n With e aircraf headin one be of t a 0 rece s a na larger or smaller that n rc d by th ther 9- t: Aiter emn fica ion and compari n. the cutest. o volt e comparison circuit l1 onsists gt a voltage Whose magnitude is proportional .0 the difierence in the energy content of the two received signals, and the pointer of indicating meter l8 moves to the right or left depending 3 on the position of the signal transmitter relative to the airplane heading.

Antenna i9, receiver I 5, video amplifier I3 and blocking oscillator I9 are of conventional design. Diode remembering circuits i5 and 56 each consists of a diode tube 22 and a storage condenser 23 which charges to a value approximately equal to the peak value of the video signal voltage each time lobe switch 14 connects circuit I5 or I6 to video amplifier I3. In order that meter I8 will give a correct indication of aircraft orientation even though a signal is not continuously present as would be the case when intermittent signals are being received, the storage condensers in circuits I5 and I6 are not shunted by resistors.

Normally these condensers have no path through which to discharge; therefore, they remain charged to substantially the value at which the last signal had charged them, and the indicator of meter 59 remains at the position determined by the charge on the condensers. Thus a remembering characteristic is present in circuits I5 and I6.

In order that the storage condensers of circuits i5 and I6 may be charged up to a new value, they are quickly discharged by the operation of circuits I9, 29 and 2 E. Each time a new burst of video signal is applied to blocking oscillator I8, discharge circuits and El are triggered and provide discharge paths for the storage condensers in circuits I5 and E6. These storage condensers are then ready to receive new values of charge supplied by the remainder of the burst of signal.

Discharge circuits 20 and 2| each comprises a sig- To illustrate the operation of these discharge 7 circuits, remembering circuits and oscillator circuits, a specific application of a device embodying the principles of this invention will be given.

Suppose a direction finding system as herein disclosed, received signals from a pulsed radio frequency transmitter which employed a directional antenna which rotated in azimuth. Each time the azimuth sweeping, transmitter antenna pointed toward the direction finding system, a burst of signals would be received by the direction finding system. Upon the reception of the first pulse of this burst of signals, blocking oscillator I9 would trigger the discharge circuits 20 and 2 I, and diode remembering circuits I5 and I6 would be discharged. During the remainder of the time in which the transmitter antenna was pointed in the general direction of the direction finding system, the act of lobe switching in the direction finding system would occur several times and each of diode remembering circuits I5 and It would acquire a new value of electrical charge. The time constant of these remembering circuits is sufliciently large so that meter I8 would retain its indication until the transmitter antenna had rotated through approximately 360 degrees in azimuth and again pointed in the general direction of the direction finding system. At this time, a new burst of signals would be received by the direction finding system, and blocking oscillator I9 would trigger discharge circuits 20 and 2|, which in turn, would discharge diode remembering circuits I5 and I6. Circuits I5 and I6 then again acquire new values of electrical charge.

Blocking oscillator I 9 has a long time constant, of the order of seconds rather than microseconds. Consequently oscillator I9 is not triggered by each individual pulse when pulsed signals are being received.

Diode remembering circuits I5 and I 6 also have very; long time constants and retain their values of charge until discharged by the action of oscillator I9 and discharge circuits 20 and 2|.

While there has been here described what is at present considered to be the preformed embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention.

What is claimed is:

A reception system for indicating the direction of intermittent bursts of radio-frequency signals, said system comprising a lobe switching antenna having first switching means for shifting the lobe thereof between two predetermined angular positions at a rate such that said lobe is shifted a plurality of times in the interval of a burst, a receiver having its input coupled to said antenna, first and second remembering circuits each of which derives a steady direct current voltage having a magnitude proportional to the peak amplitude of an intermittent signal applied thereto, second switching means synchronized with said first switching means for selectively applying the output of said receiver to said respective first and second remembering circuits, indicator means coupled to both said first and second remembering circuits for indicating the difierence between the magnitudes of the direct current voltages from said first and second remembering circuits, and discharging means coupled between said receiver and said first and second remembering circuits for dissipating the direct current voltages of both said first and second remembering circuits in response to the initiation of a received burst of signal, whereby said indicator means continuously provides an indication of the bearing of each successive burst of radio-frequency signal.

PAUL A. PEARSON.

References Cited in the file Of this patent UNITED STATES PATENTS Number Name Date 2,176,469 Moueix Oct. 17, 1939 2,189,549 Hershberger Feb. 6, 1940 2,266,038 Hinman Dec. 16, 1941 2,392,420 Steinhofi Jan. 8, 1946 2,405,930 Goldberg Aug. 13, 1946 2,415,566 Rhea Feb. 11, 1947 2,418,143 Stodola Apr. 1, 1947 2,422,072 Blodgett June 10, 1947 2,449,517 Stout et a1. Sept. 14, 1948 2,539,402 Clark Jan. 30, 1951 

